Formed during the reduction of molecular oxygen or water oxidation, reactive oxygen species (ROS) are produced by a variety of enzymes and redox reactions in almost every compartment of the plant cell. In addition to causing cellular damage, these ROS play a role in signaling networks. Many factors contribute to and, simultaneously, control their metabolism, and it is difficult to detect individual ROS accurately. This is due to several challenges inherent to ROS-their relatively short half-lives, low intracellular concentrations, enzymatic and non-enzymatic scavenging capacity of the cells, and the absence of absolutely selective probes for ROS. Here, we describe the common approaches taken for detecting primary ROS, singlet oxygen, superoxide, and hydrogen peroxide as we discuss their advantages and limitations. We can conclude that using two or more independent methods that yield similar results for detection is a reliable means for studying ROS in intact plant tissues.